This work was supported by the following grants to Eva Sevick: NIH R01 CA128919 and NIH R01 HL092923.

All animal studies were performed in accordance with the standards of the University of Texas Health Science Center (Houston, TX), Department of Comparative Medicine, and Center for Molecular Imaging after review and approval of the protocol by their respective Institutional Animal Care and Use Committee (IACUC) or Animal Welfare Committee (AWC).
1. Preparation of Animals 24 Hr Prior to Imaging
The steps below must be done (as needed) the day before lymphatic imaging takes place.
<ol>
	<li>Place animal in an induction box and sedate with isoflurane.</li>
	<li>Once the animal is in a state of profound anesthesia (monitored with toe-pinch maneuver), place sedated animal on a diaper/fluff pad and position nose in a nose cone connected to isoflurane gas.</li>
	<li>Clip all hair/fur (if any) around the area to be imaged.</li>
	<li>Apply depilatory agent (NAIR) to the clipped area and leave it on the skin for up to 3 min.</li>
	<li>Gently wipe off all depilatory agent with warm, damp gauze or paper towel.</li>
	<li>Gently rinse the skin with warm water and gently dry the area with gauze or paper towel.</li>
	<li>Allow animals to recover on a heating pad or under a heat lamp, and return to their cage.</li>
</ol>
2. Day of Imaging
<ol>
	<li>Reconstitute imaging agent with sterile water, then dilute using sterile, normal (0.85%) saline to achieve 645 &mu;M (5 &mu;g/10 &mu;l) for ICG or 200 &mu;M (6.8 &mu;g/10 &mu;l) for cABD-IRDye800. Keep solutions in dark conditions and use within 6 hr of reconstitution.</li>
	<li>Place animal in an induction box and sedate with isoflurane.</li>
	<li>Once the animal is in a state of profound anesthesia (monitored with toe-pinch maneuver), place sedated animal on its side on a diaper/fluff pad and position nose in a nose cone connected to gas isoflurane.</li>
	<li>Turn off the lights (so the room is dark). If needed, a small desk halogen light can be used for a small amount of light to see injections.</li>
	<li>Using an insulin syringe with a 31-gauge needle, inject ID 5 &mu;l to 50 &mu;l of ICG or cABD-IRDye800 in the dorsal aspect of each hind paw and/or on the left and right side of the base of the tail, depending on the area of interest (see Discussion). Each injected dose may range from 0.083 to 1.25 mg/kg (ICG) or 0.113 to 1.7 mg/kg (cABD-IRDye800). Injection volumes will vary with animal strain and injection site. For athymic mice, the volume of injection can be 5 &mu;l (hind paw) or 10 &mu;l (base of tail). If animal is not under the imaging system for the injection(s), place the animal under the imaging system immediately after the injection(s).</li>
	<li>If no dye uptake is seen in the lymphatics, step 2.5 will need to be repeated as needed per animal protocol.</li>
	<li>Once lymphatics are seen, cover the injection site with black electrical tape or black paper.</li>
	<li>Acquire lymphatic images for up to 1 hr using V++ software and a small animal, NIRF imaging system. (Animals are sedated with isoflurane and respirations are monitored while images are acquiring.) While small animal, NIRF imagers are commercially available, we utilize a customized, small animal NIRF imaging system consisting of a 785-nm laser diode (1005-9mm-78503, Intense, North Brunswick, NJ) outfitted with an aspheric lens (C24TME-B, Thorlabs, Newton, NJ), diffuser (ED1-C20, Thorlabs), and filter (LD01-785/10-25, Semrock, Rochester, NY) to create a uniform excitation field that illuminates the animal at an incident fluence rate of less than 1.4 mW per square centimeter10. An electron multiplying charged-coupled device (EMCCD, PhotonMax512, Princeton Instruments, Trenton, NJ) camera system with two 830-nm filters (AND11333, Andover Corp., Salem, NH) and a 28-mm Nikkor lens (1992, Nikon, Melville, NY) is used to capture lymphatic images with integration times of 200 msec for dynamic imaging and 800 msec for static imaging5. See Figure 1 for system configuration, the Table for additional details of each component, and the Discussion for a brief discussion of key imager properties.</li>
	<li>Allow animals to recover on a heating pad or under a heat lamp and return to their cage, or euthanize.</li>
	<li>Analyze images using ImageJ or MATLAB software. See Figure 6.</li>
</ol>

<ol>
	<li>Alitalo, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+lymphatic+vasculature+in+disease.">The lymphatic vasculature in disease.</a> Nat. Med. 17, 1371-1380 (2011).</li><li>Rasmussen, J. C., Tan, I. C., Marshall, M. V., Fife, C. E., Sevick-Muraca, E. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lymphatic+imaging+in+humans+with+near-infrared+fluorescence.">Lymphatic imaging in humans with near-infrared fluorescence.</a> Curr. Opin. Biotechnol. 20, 74-82 (2009).</li><li>Rasmussen, J. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+Lymphatic+Architecture+and+Dynamic+Transport+Imaged+Using+Near-infrared+Fluorescence.">Human Lymphatic Architecture and Dynamic Transport Imaged Using Near-infrared Fluorescence.</a> Transl. Oncol. 3, 362-372 (2010).</li><li>Sevick-Muraca, E. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Translation+of+near-infrared+fluorescence+imaging+technologies:+emerging+clinical+applications.">Translation of near-infrared fluorescence imaging technologies: emerging clinical applications.</a> Annu. Rev. Med. 63, 217-231 (2012).</li><li>Kwon, S., Sevick-Muraca, E. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Noninvasive+quantitative+imaging+of+lymph+function+in+mice.">Noninvasive quantitative imaging of lymph function in mice.</a> Lymphat. Res. Biol. 5, 219-231 (2007).</li><li>Kwon, S., Sevick-Muraca, E. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mouse+phenotyping+with+near-infrared+fluorescence+lymphatic+imaging.">Mouse phenotyping with near-infrared fluorescence lymphatic imaging.</a> Biomed Opt Express. 2, 1403-1411 (2011).</li><li>Marshall, M. V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Near-infrared+fluorescence+imaging+in+humans+with+indocyanine+green:+a+review+and+update.">Near-infrared fluorescence imaging in humans with indocyanine green: a review and update.</a> The Open Surgical Oncology Journal. 2, 12-25 (2010).</li><li>Davies-Venn, C. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Albumin-Binding+Domain+Conjugate+for+Near-Infrared+Fluorescence+Lymphatic+Imaging.">Albumin-Binding Domain Conjugate for Near-Infrared Fluorescence Lymphatic Imaging.</a> Mol. Imaging Biol. , (2011).</li><li>Sharma, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+imaging+of+lymph+function.">Quantitative imaging of lymph function.</a> Am. J. Physiol. Heart Circ. Physiol. 292, 3109-3118 (2007).</li><li>Kwon, S., Sevick-Muraca, E. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+lymphatic+imaging+in+tumor-bearing+mice.">Functional lymphatic imaging in tumor-bearing mice.</a> J. Immunol. Methods. 360, 167-172 (2010).</li><li>Karlsen, T. V., McCormack, E., Mujic, M., Tenstad, O., Wiig, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Minimally+invasive+quantification+of+lymph+flow+in+mice+and+rats+by+imaging+depot+clearance+of+near-infrared+albumin.">Minimally invasive quantification of lymph flow in mice and rats by imaging depot clearance of near-infrared albumin.</a> Am. J. Physiol. Heart Circ. Physiol. 302, 391-401 (2012).</li><li>Zhou, Q., Wood, R., Schwarz, E. M., Wang, Y. J., Xing, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Near-infrared+lymphatic+imaging+demonstrates+the+dynamics+of+lymph+flow+and+lymphangiogenesis+during+the+acute+versus+chronic+phases+of+arthritis+in+mice.">Near-infrared lymphatic imaging demonstrates the dynamics of lymph flow and lymphangiogenesis during the acute versus chronic phases of arthritis in mice.</a> Arthritis Rheum. 62, 1881-1889 (2010).</li><li>Adams, K. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+evidence+of+lymphatic+function+improvement+after+advanced+pneumatic+compression+device+treatment+of+lymphedema.">Direct evidence of lymphatic function improvement after advanced pneumatic compression device treatment of lymphedema.</a> Biomed. Opt. Express. 1, 114-125 (2010).</li><li>Tan, I. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+of+lymphatic+contractile+function+after+manual+lymphatic+drainage+using+near-infrared+fluorescence+imaging.">Assessment of lymphatic contractile function after manual lymphatic drainage using near-infrared fluorescence imaging.</a> Arch. Phys. Med. Rehabil. 92, 756-764 (2011).</li><li>Lapinski, P. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=RASA1+maintains+the+lymphatic+vasculature+in+a+quiescent+functional+state+in+mice.">RASA1 maintains the lymphatic vasculature in a quiescent functional state in mice.</a> J. Clin. Invest. 122, 733-747 (2012).</li><li>Maus, E. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Near-infrared+fluorescence+imaging+of+lymphatics+in+head+and+neck+lymphedema.">Near-infrared fluorescence imaging of lymphatics in head and neck lymphedema.</a> Head Neck. 34, 448-453 (2012).</li><li>Galanzha, E. I., Tuchin, V. V., Zharov, V. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Advances+in+small+animal+mesentery+models+for+in+vivo+flow+cytometry,+dynamic+microscopy,+and+drug+screening.">Advances in small animal mesentery models for in vivo flow cytometry, dynamic microscopy, and drug screening.</a> World J. Gastroenterol. 13, 192-218 (2007).</li><li>Schramm, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+cervical+lymph+node+preparation:+a+novel+approach+to+study+lymphocyte+homing+by+intravital+microscopy.">The cervical lymph node preparation: a novel approach to study lymphocyte homing by intravital microscopy.</a> Inflammation research : official journal of the European Histamine Research Society. 55, 160-167 (2006).</li><li>Hall, M. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imaging+prostate+cancer+lymph+node+metastases+with+a+multimodality+contrast+agent.">Imaging prostate cancer lymph node metastases with a multimodality contrast agent.</a> Prostate. 72, 129-146 (2012).</li><li>Zhu, B., Sevick-Muraca, E. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Minimizing+excitation+leakage+and+maximizing+measurement+sensitivity+for+molecular+imaging+with+near-infrared+fluorescence.">Minimizing excitation leakage and maximizing measurement sensitivity for molecular imaging with near-infrared fluorescence.</a> J. Innovat. Opt. Health Sci. 4, 301-307 (2011).</li></ol>

Authors have nothing to disclose, but some authors are listed on a patent.

We use a custom, small animal NIRF imaging system to capture images of labeled lymph vessels in mice. To construct movies of lymph movement, 300 or more images are collected. For functional analysis of lymphatics from movies, two or more ROIs are manually drawn along a lymph vessel. The dimensions of the ROIs are kept constant for each vessel and are approximately the diameter of the vessel. While whole animal spatial resolution can depict fluorescent lymphatic vessels of 100 microns or less, a macrolens for fine...

<table border="1">
 <tbody>
 <tr>
 <td>Solutions, Reagents, and Equipment</td>
 <td>Company</td>
 <td>Catalog Number</td>
 <td>Comments </td>
 </tr>
 <tr>
 <td>Indocyanine green (ICG)</td>
 <td>Patheon Italia S.P.A.</td>
 <td>NDC 25431-424-02</td>
 <td>Reconstitute to 645 &mu;M (5 &mu;g/10 &mu;L)</td>
 </tr>
 <tr>
 <td>Cyclic Albumin Binding Domain(cABD) </td>
 <td>Bachem</td>
 <td>Custom</td>
 <td>Reconstitute to 200 &mu;M (6.8 &mu;g/10 &mu;L) </td>
 </tr>
 <tr>
 <td>IRDye800</td>
 <td>Li-COR</td>
 <td>IRDye 800CW</td>
 <td>Reconstitute according to manufacture's instructions; conjugate with cABD at equilmolar concentrations </td>
 </tr>
 <tr>
 <td>Sterile Water</td>
 <td>Hospira, Inc., Lake Forest, IL </td>
 <td>NDC 0409-4887-10</td>
 <td></td>
 </tr>
 <tr>
 <td>NAIR</td>
 <td>Church &amp; Dwight Co., Inc.</td>
 <td>Local Stores</td>
 <td><a href="http://www.nairlikeneverbefore.com" target="_blank">www.nairlikeneverbefore.com</a> </td>
 </tr>
 <tr>
 <td>Imaging System (components below)</td>
 <td>Center for Molecular Imaging</td>
 <td>N/A</td>
 <td>Custom-built in our laboratories.</td>
 </tr>
 <tr>
 <td>Electron-multiplying charge-coupled device (EMCCD) camera</td>
 <td>Princeton Instruments, Trenton, NJ</td>
 <td>Photon Max 512</td>
 <td></td>
 </tr>
 <tr>
 <td>Nikon camera lens</td>
 <td>Nikon Inc., Melville, NY</td>
 <td>Model No. 1992, Nikkor 28mm</td>
 <td></td>
 </tr>
 <tr>
 <td>Optical filter </td>
 <td>Andover Corp., Salem,NH</td>
 <td>ANDV11333</td>
 <td>Two 830.0/10.0 nm bandpass filters are used in front of lens</td>
 </tr>
 <tr>
 <td>785-nm laser diode</td>
 <td>Intense Ltd, North Brunswick, NJ</td>
 <td>1005-9MM-78503</td>
 <td>500 mW of optical output</td>
 </tr>
 <tr>
 <td>Collimating optics</td>
 <td>Thorlabs, Newton, NJ</td>
 <td>C240TME-B</td>
 <td>Collimates laser output prior to cleanup filter</td>
 </tr>
 <tr>
 <td>Clean-up filter</td>
 <td>Semrock, Inc., Rochester, NY</td>
 <td>LD01-785/10-25</td>
 <td>Removes laser emission in fluorescence band</td>
 </tr>
 <tr>
 <td>Optical diffuser</td>
 <td>Thorlabs, Newton, NJ</td>
 <td>ED1-C20</td>
 <td>Diffuses the laser over the animal</td>
 </tr>
 <tr>
 <td>V++</td>
 <td>Digital Optics, Browns Bay, Auckland, New Zealand</td>
 <td>Version 5.0</td>
 <td>Software used to control camera system and save images to computer. <a href="http://digitaloptics.net/" target="_blank">http://digitaloptics.net/</a> </td>
 </tr>
 <tr>
 <td></td>
 <td></td>
 <td></td>
 <td>Analytic Software Either of the following software packages can be used for image analysis</td>
 </tr>
 <tr>
 <td> ImageJ</td>
 <td>National Institutes of Health, Bethesda, MD</td>
 <td>Most current version available </td>
 <td>Freeware available at <a href="http://rsbweb.nih.gov/ij/" target="_blank">http://rsbweb.nih.gov/ij/</a></td>
 </tr>
 <tr>
 <td> MATLAB</td>
 <td>MathWorks, Natick, MA</td>
 <td>Version 2008a or later</td>
 <td><a href="http://www.mathworks.com/" target="_blank">http://www.mathworks.com/</a></td>
 </tr>
 </tbody>
</table>

non-invasive optical imaging of the lymphatic vasculature of a mouse

The lymphatic vascular system is an important component of the circulatory system that maintains fluid homeostasis, provides immune surveillance, and mediates fat absorption in the gut. Yet despite its critical function, there is comparatively little understanding of how the lymphatic system adapts to serve these functions in health and disease1. Recently, we have demonstrated the ability to dynamically image lymphatic architecture and lymph "pumping" action in normal human subjects as well as in persons suffering lymphatic dysfunction using trace administration of a near-infrared fluorescent (NIRF) dye and a custom, Gen III-intensified imaging system2-4. NIRF imaging showed dramatic changes in lymphatic architecture and function with human disease. It remains unclear how these changes occur and new animal models are being developed to elucidate their genetic and molecular basis. In this protocol, we present NIRF lymphatic, small animal imaging5,6 using indocyanine green (ICG), a dye that has been used for 50 years in humans7, and a NIRF dye-labeled cyclic albumin binding domain (cABD-IRDye800) peptide that preferentially binds mouse and human albumin8. Approximately 5.5 times brighter than ICG, cABD-IRDye800 has a similar lymphatic clearance profile and can be injected in smaller doses than ICG to achieve sufficient NIRF signals for imaging8. Because both cABD-IRDye800 and ICG bind to albumin in the interstitial space8, they both may depict active protein transport into and within the lymphatics. Intradermal (ID) injections (5-50 &mu;l) of ICG (645 &mu;M) or cABD-IRDye800 (200 &mu;M) in saline are administered to the dorsal aspect of each hind paw and/or the left and right side of the base of the tail of an isoflurane-anesthetized mouse. The resulting dye concentration in the animal is 83-1,250 &mu;g/kg for ICG or 113-1,700 &mu;g/kg for cABD-IRDye800. Immediately following injections, functional lymphatic imaging is conducted for up to 1 hr using a customized, small animal NIRF imaging system. Whole animal spatial resolution can depict fluorescent lymphatic vessels of 100 microns or less, and images of structures up to 3 cm in depth can be acquired9. Images are acquired using V++ software and analyzed using ImageJ or MATLAB software. During analysis, consecutive regions of interest (ROIs) encompassing the entire vessel diameter are drawn along a given lymph vessel. The dimensions for each ROI are kept constant for a given vessel and NIRF intensity is measured for each ROI to quantitatively assess "packets" of lymph moving through vessels.

Example of NIRF Lymphatic Imaging in Mice
When ICG or cABD-IRDye800 is injected ID at the base of the tail of a normal mouse, the lymphatic vasculature between the injection site at the base of the tail and the inguinal lymph node (LN) should be immediately visualized. Shortly after injection (a few seconds to minutes), the lymphatic vessel between the inguinal LN and the axillary LN should be visualized as seen in Figure 2. Since the lymphatics in mice vary from animal to animal...

Watch this Scientific Journal Video about Non-invasive Optical Imaging of the Lymphatic Vasculature of a Mouse at JoVE.com

Non-invasive Optical Imaging of the Lymphatic Vasculature of a Mouse

Recently developed imaging techniques using near-infrared fluorescence (NIRF) may help elucidate the role the lymphatic system plays in cancer metastasis, immune response, wound repair, and other lymphatic-associated diseases.

The lymphatic  vascular system is an important component of the circulatory system that  maintains fluid homeostasis, provides immune surveillance, and ...

non-invasive-optical-imaging-of-the-lymphatic-vasculature-of-a-mouse

Research

JoVE Journal

Immunology and Infection

16.0K Views.  University of Texas Health Science Center-Houston. Recently developed imaging techniques using near-infrared fluorescence (NIRF) may help elucidate the role the lymphatic system plays in cancer metastasis, immune response, wound repair, and other lymphatic-associated diseases.

Video: Non-invasive Optical Imaging of the Lymphatic Vasculature of a Mouse

Non-invasive Imaging of Leukocyte Homing and Migration in vivo

Two-photon (2P) microscopy is a high resolution imaging technique that has been broadly adapted by biologists. The value of 2P microscopy is that it provides rich spatiotemporal information regarding cell behaviors within intact tissues and in live mice. Leukocyte recruitment plays a significant role in host defense against infection and when unchecked, can contribute to inflammatory and autoimmune diseases. Studying leukocyte recruitment in vivo is technically challenging since cells are moving rapidly within vessels located deep within light scattering tissues. To date, most intravital imaging studies require surgical preparation to expose the blood vessels and tissues. To avoid the tissue damage and inflammation induced by surgery itself, here, we describe a non-invasive single-cell imaging approach that can be used to study leukocyte trafficking in the mouse footpad and phalanges. We discuss the technical aspects of our 2P imaging preparation and walk the reader through a typical experiment from initial set up to execution and data collection.

Non-invasive Imaging of Leukocyte Homing and Migration in vivo

Here, we describe a non-invasive two-photon (2P) microscopy approach to study leukocyte homing in the mouse footpad. We discuss the technical aspects of our tissue imaging preparation and walk the reader through a typical experiment from initial set up to execution and data collection.

Two-photon (2P) microscopy is a high resolution imaging technique that has been broadly adapted by biologists.  The value of 2P microscopy is that it ...

Use of an Optical Trap for Study of Host-Pathogen Interactions for Dynamic Live Cell Imaging

Dynamic live cell imaging allows direct visualization of real-time interactions between cells of the immune system1, 2; however, the lack of spatial and temporal control between the phagocytic cell and microbe has rendered focused observations into the initial interactions of host response to pathogens difficult. Historically, intercellular contact events such as phagocytosis3 have been imaged by mixing two cell types, and then continuously scanning the field-of-view to find serendipitous intercellular contacts at the appropriate stage of interaction. The stochastic nature of these events renders this process tedious, and it is difficult to observe early or fleeting events in cell-cell contact by this approach. This method requires finding cell pairs that are on the verge of contact, and observing them until they consummate their contact, or do not. To address these limitations, we use optical trapping as a non-invasive, non-destructive, but fast and effective method to position cells in culture.
Optical traps, or optical tweezers, are increasingly utilized in biological research to capture and physically manipulate cells and other micron-sized particles in three dimensions4. Radiation pressure was first observed and applied to optical tweezer systems in 19705, 6, and was first used to control biological specimens in 19877. Since then, optical tweezers have matured into a technology to probe a variety of biological phenomena8-13.
We describe a method14 that advances live cell imaging by integrating an optical trap with spinning disk confocal microscopy with temperature and humidity control to provide exquisite spatial and temporal control of pathogenic organisms in a physiological environment to facilitate interactions with host cells, as determined by the operator. Live, pathogenic organisms like Candida albicans and Aspergillus fumigatus, which can cause potentially lethal, invasive infections in immunocompromised individuals15, 16 (e.g. AIDS, chemotherapy, and organ transplantation patients), were optically trapped using non-destructive laser intensities and moved adjacent to macrophages, which can phagocytose the pathogen. High resolution, transmitted light and fluorescence-based movies established the ability to observe early events of phagocytosis in living cells. To demonstrate the broad applicability in immunology, primary T-cells were also trapped and manipulated to form synapses with anti-CD3 coated microspheres in vivo, and time-lapse imaging of synapse formation was also obtained. By providing a method to exert fine spatial control of live pathogens with respect to immune cells, cellular interactions can be captured by fluorescence microscopy with minimal perturbation to cells and can yield powerful insight into early responses of innate and adaptive immunity.

A method is described to individually select, manipulate, and image live pathogens using an optical trap coupled to a spinning disk microscope. The optical trap provides spatial and temporal control of organisms and places them adjacent to host cells. Fluorescence microscopy captures dynamic intercellular interactions with minimal perturbation to cells.

Dynamic live cell imaging allows direct visualization of real-time interactions between cells of the immune system1, 2; however, the lack of spatial and ...

A Method for Labeling Vasculature in Embryonic Mice

The establishment of a functional blood vessel network is an essential part of organogenesis, and is required for optimal organ function. For example, in the thymus proper vasculature formation and patterning is essential for thymocyte entry into the organ and mature T-cell exit to the periphery. The spatial arrangement of blood vessels in the thymus is dependent upon signals from the local microenvironment, namely thymic epithelial cells (TEC). Several recent reports suggest that disruption of these signals results in thymus blood vessel defects 1,2. Previous studies have described techniques used to label the neonatal and adult thymus vasculature 1,2. We demonstrate here a technique for labeling blood vessels in the embryonic thymus. This method combines the use of FITC-dextran or Griffonia (Bandeiraea) Simplicifolia Lectin I (GSL 1 - isolectin B4) facial vein injections and CD31 antibody staining to identify thymus vascular structures and PDGFR-&beta; to label thymic perivascular mesenchyme 3-5. The option of using cryosections or vibratome sections is also provided. This protocol can be used to identify thymus vascular defects, which is critical for defining the roles of TEC-derived molecules in thymus blood vessel formation. As the method labels the entire vasculature, it can also be used to analyze the vascular networks in multiple organs and tissues throughout the embryo including skin and heart 6-10.

This article describes a method for labeling embryonic skin and thymus blood vessels.

The establishment of a functional blood vessel network is an essential part of organogenesis, and is required for optimal organ function. For example, in ...

Intravital Imaging of the Mouse Popliteal Lymph Node

Lymph nodes (LNs) are secondary lymphoid organs, which are strategically located throughout the body to allow for trapping and presentation of foreign antigens from peripheral tissues to prime the adaptive immune response. Juxtaposed between innate and adaptive immune responses, the LN is an ideal site to study immune cell interactions1,2. Lymphocytes (T cells, B cells and NK cells), dendritic cells (DCs), and macrophages comprise the bulk of bone marrow-derived cellular elements of the LN. These cells are strategically positioned in the LN to allow efficient surveillance of self antigens and potential foreign antigens3-5. The process by which lymphocytes successfully encounter cognate antigens is a subject of intense investigation in recent years, and involves an integration of molecular contacts including antigen receptors, adhesion molecules, chemokines, and stromal structures such as the fibro-reticular network2,6-12. 
Prior to the development of high-resolution real-time fluorescent in vivo imaging, investigators relied on static imaging, which only offers answers regarding morphology, position, and architecture. While these questions are fundamental in our understanding of immune cell behavior, the limitations intrinsic with this technique does not permit analysis to decipher lymphocyte trafficking and environmental clues that affect dynamic cell behavior. Recently, the development of intravital two-photon laser scanning microscopy (2P-LSM) has allowed investigators to view the dynamic movements and interactions of individual cells within live LNs in situ12-16. In particular, we and others have applied this technique to image cellular behavior and interactions within the popliteal LN, where its compact, dense nature offers the advantage of multiplex data acquisition over a large tissue area with diverse tissue sub-structures11,17-18. It is important to note that this technique offers added benefits over explanted tissue imaging techniques, which require disruption of blood, lymph flow, and ultimately the cellular dynamics of the system. Additionally, explanted tissues have a very limited window of time in which the tissue remains viable for imaging after explant. With proper hydration and monitoring of the animal's environmental conditions, the imaging time can be significantly extended with this intravital technique. Here, we present a detailed method of preparing mouse popliteal LN for the purpose of performing intravital imaging.

Recent advances in 2-photon microscopy have enabled real-time in situ imaging of live tissues in animal models, thereby enhancing our ability to investigate cellular behavior in both physiologic and pathologic conditions. Here, we outline the preparations required to perform intravital imaging of the mouse popliteal lymph node.

Lymph nodes (LNs) are secondary lymphoid organs, which are strategically located throughout the body to allow for trapping and presentation of foreign ...

Non-invasive Imaging of Disseminated Candidiasis in Zebrafish Larvae

Disseminated candidiasis caused by the pathogen Candida albicans is a clinically important problem in hospitalized individuals and is associated with a 30 to 40% attributable mortality6. Systemic candidiasis is normally controlled by innate immunity, and individuals with genetic defects in innate immune cell components such as phagocyte NADPH oxidase are more susceptible to candidemia7-9. Very little is known about the dynamics of C. albicans interaction with innate immune cells in vivo. Extensive in vitro studies have established that outside of the host C. albicans germinates inside of macrophages, and is quickly destroyed by neutrophils10-14. In vitro studies, though useful, cannot recapitulate the complex in vivo environment, which includes time-dependent dynamics of cytokine levels, extracellular matrix attachments, and intercellular contacts10, 15-18. To probe the contribution of these factors in host-pathogen interaction, it is critical to find a model organism to visualize these aspects of infection non-invasively in a live intact host. 
The zebrafish larva offers a unique and versatile vertebrate host for the study of infection. For the first 30 days of development zebrafish larvae have only innate immune defenses2, 19-21, simplifying the study of diseases such as disseminated candidiasis that are highly dependent on innate immunity. The small size and transparency of zebrafish larvae enable imaging of infection dynamics at the cellular level for both host and pathogen. Transgenic larvae with fluorescing innate immune cells can be used to identify specific cells types involved in infection22-24. Modified anti-sense oligonucleotides (Morpholinos) can be used to knock down various immune components such as phagocyte NADPH oxidase and study the changes in response to fungal infection5. In addition to the ethical and practical advantages of using a small lower vertebrate, the zebrafish larvae offers the unique possibility to image the pitched battle between pathogen and host both intravitally and in color. 
The zebrafish has been used to model infection for a number of human pathogenic bacteria, and has been instrumental in major advances in our understanding of mycobacterial infection3, 25. However, only recently have much larger pathogens such as fungi been used to infect larva5, 23, 26, and to date there has not been a detailed visual description of the infection methodology. Here we present our techniques for hindbrain ventricle microinjection of prim25 zebrafish, including our modifications to previous protocols. Our findings using the larval zebrafish model for fungal infection diverge from in vitro studies and reinforce the need to examine the host-pathogen interaction in the complex environment of the host rather than the simplified system of the Petri dish5.

The rapid development, small size and transparency of zebrafish are tremendous advantages for the study of innate immune control of infection1-4. Here we demonstrate techniques for infecting zebrafish larvae using the fungal pathogen Candida albicans by microinjection, methodology recently used to implicate phagocyte NADPH oxidase activity in control of fungal dimorphism5.

Disseminated candidiasis caused by the pathogen Candida albicans is a clinically important problem in hospitalized individuals and is associated with a 30 ...

Non-Invasive Model of Neuropathogenic Escherichia coli Infection in the Neonatal Rat

Investigation of the interactions between animal host and bacterial pathogen is only meaningful if the infection model employed replicates the principal features of the natural infection. This protocol describes procedures for the establishment and evaluation of systemic infection due to neuropathogenic Escherichia coli K1 in the neonatal rat. Colonization of the gastrointestinal tract leads to dissemination of the pathogen along the gut-lymph-blood-brain course of infection and the model displays strong age dependency. A strain of E. coli O18:K1 with enhanced virulence for the neonatal rat produces exceptionally high rates of colonization, translocation to the blood compartment and invasion of the meninges following transit through the choroid plexus. As in the human host, penetration of the central nervous system is accompanied by local inflammation and an invariably lethal outcome. The model is of proven utility for studies of the mechanism of pathogenesis, for evaluation of therapeutic interventions and for assessment of bacterial virulence.

Non-Invasive Model of Neuropathogenic Escherichia coli Infection in the Neonatal Rat

Here, a procedure is described for the establishment of systemic infection in the neonatal rat with cultures of Escherichia coli K1. This non-invasive procedure permits colonization of the gastrointestinal tract, translocation of the pathogen to the systemic circulation, and invasion of the central nervous system at the choroid plexus.

Investigation of the interactions between animal host and bacterial pathogen is only meaningful if the infection model employed replicates the principal ...

Complete Thymectomy in Adult Rats with Non-invasive Endotracheal Intubation

Thymectomy in neonatal rodents is an established and reliable procedure for immunological studies. However, in adult rats, complications of hemorrhage and pneumothorax from pleural disruption can result in a significant mortality rate. This protocol is a simple method of rat thymectomy that utilizes a mini-sternotomy and endotracheal intubation. Intubation is accomplished with a non-invasive and easily reproducible method and allows for positive pressure ventilation to prevent pneumothorax and a controlled airway that allows sufficient time for careful thymus dissection to minimize pleural disruption. A 1.5 cm sternal incision decreases contact with mediastinal vessels and pleura, while still providing full visualization of the thymus. Following exposure of the mediastinum, the thymus is removed by blunt dissection under magnification. The pleural space is then sealed by suture closure of the pre-tracheal muscles followed by the application of surgical glue. The thorax is then closed by suture closure of the sternum, followed by suture closure of the skin. All thymectomies were complete as evidenced by immunohistochemical (IHC) staining of mediastinal tissue, and absence of na&#239;ve T-cells by flow cytometry, and the procedure had a 96% survival rate. This method is suitable when complete thymectomy with minimal complications is desired for further immunological studies in athymic adult rats.

Rodent thymectomy is a valuable technique in immunological research. Here, a protocol for complete thymectomy in adult rats using a mini-sternotomy along with non-invasive intubation and positive pressure ventilation to minimize perioperative morbidity and mortality is described.

Thymectomy in neonatal rodents is an established and reliable procedure for immunological studies. However, in adult rats, complications of hemorrhage and ...

Non-invasive Imaging of the Innate Immune Response in a Zebrafish Larval Model of Streptococcus iniae Infection

The aquatic pathogen, Streptococcus iniae, is responsible for over 100 million dollars in annual losses for the aquaculture industry and is capable of causing systemic disease in both fish and humans. A better understanding of S. iniae disease pathogenesis requires an appropriate model system. The genetic tractability and the optical transparency of the early developmental stages of zebrafish allow for the generation and non-invasive imaging of transgenic lines with fluorescently tagged immune cells. The adaptive immune system is not fully functional until several weeks post fertilization, but zebrafish larvae have a conserved vertebrate innate immune system with both neutrophils and macrophages. Thus, the generation of a larval infection model allows the study of the specific contribution of innate immunity in controlling S. iniae infection.
The site of microinjection will determine whether an infection is systemic or initially localized. Here, we present our protocols for otic vesicle injection of zebrafish aged 2-3 days post fertilization as well as our techniques for fluorescent confocal imaging of infection. A localized infection site allows observation of initial microbe invasion, recruitment of host cells and dissemination of infection. Our findings using the zebrafish larval model of S. iniae infection indicate that zebrafish can be used to examine the differing contributions of host neutrophils and macrophages in localized bacterial infections. In addition, we describe how photolabeling of immune cells can be used to track individual host cell fate during the course of infection.

Non-invasive Imaging of the Innate Immune Response in a Zebrafish Larval Model of Streptococcus iniae Infection

Here, we present a protocol for the generation and imaging of a localized bacterial infection in the zebrafish otic vesicle.

The aquatic pathogen, Streptococcus iniae, is responsible for over 100 million dollars in annual losses for the aquaculture industry and is capable of ...

A Non-invasive and Technically Non-intensive Method for Induction and Phenotyping of Experimental Bacterial Pneumonia in Mice

Although community-acquired pneumonia remains a major public health problem, murine models of bacterial pneumonia have recently facilitated significant preclinical advances in our understanding of the underlying cellular and molecular pathogenesis. In vivo mouse models capture the integrated physiology and resilience of the host defense response in a manner not revealed by alternative, simplified ex vivo approaches. Several methods have been described in the literature for intrapulmonary inoculation of bacteria in mice, including aerosolization, intranasal delivery, peroral endotracheal cannulation under &#39;blind&#39; and visualized conditions, and transcutaneous endotracheal cannulation. All methods have relative merits and limitations. Herein, we describe in detail a non-invasive, technically non-intensive, inexpensive, and rapid method for intratracheal delivery of bacteria that involves aspiration (i.e., inhalation) by the mouse of an infectious inoculum pipetted into the oropharynx while under general anesthesia. This method can be used for pulmonary delivery of a wide variety of non-caustic biological and chemical agents, and is relatively easy to learn, even for laboratories with minimal prior experience with pulmonary procedures. In addition to describing the aspiration pneumonia method, we also provide step-by-step procedures for assaying the subsequent in vivo pulmonary innate immune response of the mouse, in particular, methods for quantifying bacterial clearance and the cellular immune response of the infected airway. This integrated and simple approach to pneumonia assessment allows for rapid and robust evaluation of the effect of genetic and environmental manipulations upon pulmonary innate immunity.

Several methods have been described in the literature for modeling bacterial pneumonia in mice. Herein, we describe a non-invasive, inexpensive, rapid method for inducing pneumonia via aspiration (i.e., inhalation) of a bacterial inoculum pipetted into the oropharynx. Downstream methods for assessment of the pulmonary innate immune response are also detailed.

Although community-acquired pneumonia remains a major public health problem, murine models of bacterial pneumonia have recently facilitated significant ...

Non-invasive In Vivo Fluorescence Optical Imaging of Inflammatory MMP Activity Using an Activatable Fluorescent Imaging Agent

This paper describes a non-invasive method for imaging matrix metalloproteinases (MMP)-activity by an activatable fluorescent probe, via in vivo fluorescence optical imaging (OI), in two different mouse models of inflammation: a rheumatoid arthritis (RA) and a contact hypersensitivity reaction (CHR) model. Light with a wavelength in the near infrared (NIR) window (650 - 950 nm) allows a deeper tissue penetration and minimal signal absorption compared to wavelengths below 650 nm. The major advantages using fluorescence OI is that it is cheap, fast and easy to implement in different animal models.
Activatable fluorescent probes are optically silent in their inactivated states, but become highly fluorescent when activated by a protease. Activated MMPs lead to tissue destruction and play an important role for disease progression in delayed-type hypersensitivity reactions (DTHRs) such as RA and CHR. Furthermore, MMPs are the key proteases for cartilage and bone degradation and are induced by macrophages, fibroblasts and chondrocytes in response to pro-inflammatory cytokines. Here we use a probe that is activated by the key MMPs like MMP-2, -3, -9 and -13 and describe an imaging protocol for near infrared fluorescence OI of MMP activity in RA and control mice 6 days after disease induction as well as in mice with acute (1x challenge) and chronic (5x challenge) CHR on the right ear compared to healthy ears.

Non-invasive In Vivo Fluorescence Optical Imaging of Inflammatory MMP Activity Using an Activatable Fluorescent Imaging Agent

This paper explains the application of fluorescent imaging using an activatable optical imaging probe to visualize the in vivo activity of key matrix metalloproteinases in two different experimental models of inflammation.